Buoys, floating sensors, and other marine structures depend on sealed spaces to keep water out and stay afloat. A serious crack can flood those spaces and send the entire structure underwater. Engineers, therefore, need materials that can survive harsh marine conditions without sacrificing strength, low weight, or buoyancy. Stainless steel and high-density plastic are widely used for this equipment, but neither solves the problem of keeping a damaged structure afloat.
Metallic lattice structures appear well suited to that challenge because their intricate frameworks can be extremely light while retaining considerable strength. Their open architecture, however, creates a fundamental problem in water. Liquid can move freely through the interconnected spaces, eliminating the flotation advantage that their low overall density might seem to provide.
“Although metallic lattices can be incredibly light – with densities less than one-tenth the density of water – their open, interconnected spaces allow water to enter, causing them to sink,” said Dr. Jordan Noronha, lead researcher from RMIT University’s Centre for Additive Manufacturing.
“This has made these strong, lightweight structures unsuitable for marine infrastructure – until now.”
Researchers led by RMIT University addressed that weakness by 3D printing a titanium lattice composed of hollow, interconnected struts and filling those struts with polyurethane foam. The spaces surrounding the struts remain open, so water can pass through the lattice itself rather than being blocked by a sealed outer shell.
“By filling only the hollow titanium struts with polyurethane foam, we created a structure that allows water to flow through it while remaining buoyant even after significant cracking and damage,” Noronha said.
Samples remained afloat in freshwater for more than two months, providing sustained evidence of their buoyancy. According to the researchers, the work represents the first reported demonstration of a floating metal-hybrid lattice metamaterial.
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